Changes in Cerebral Blood Flow in Patients Treated With Spinal Cord Stimulation for Low Back and Leg Pain

Inclusion Criteria: * Have had one or more back surgery procedures. * Have used an active Precision SCS device for chronic low back and bilateral leg pain for at least 6 weeks. * Have bilateral leg pain. * Have a baseline VAS of \>4 (without stimulation). * Have greater than 50% reduction in pain with SCS at optimal settings * Be 18 years of age or older. * Have the cognitive and functional capability to operate the controls for the device, to comply with directions during the study, and willing to participate in all study activities. * Be capable of reading and understanding patient information materials and giving written informed consent. Exclusion Criteria: * Have any significant medical condition that is likely to interfere with study procedures or likely to confound evaluation of study endpoints. * Have undergone a surgical lead revision or had any Precision components replaced after initial implantation. * Are allergic to any of the injected media. * Are pregnant or lactating. * Have any contraindication to the PET scan procedure itself or exposure to the intravenous radioactive tracer (H215O). * Have participated in any drug or device trial in the last 4 weeks or are currently participating in another drug or device trial.